Abstract; Common to the NACA Report (23 pages) and the Book (119 pages):

In this report implications of the low tip speed design philosophy are studied with respect to
rotorcraft capable of fast cruise speed, roughly 50% higher than that of conventional helicopters.
This is done by examining effects of tip speeds on some performance and structural-weight
aspects of compounds, based on the following concepts:

"Very preliminary studies seem to indicate that placing the ABC rotors in the Synchropter position should result in a somewhat aerodynamically cleaner than the coaxial ABC, and definitely a much cleaner design than the considered single-rotor types."

"The ABC Synchropter configuration appears to have the highest potential for low SHPcr values up to the cruise speed as high as Vcr ≈ 260 knots, when the advancing tip Mach number is no higher than MAT = 0.85."

"It appears that the ABC Synchropter concept should be further investigated as a potential candidate for the quiet rotorcraft."